This application claims the benefit of Korean Application No. 2001-84396, filed Dec. 24, 2001, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to microwave ovens, and more particularly, to a microwave oven which eliminates noise to a satisfactory standard while enduring strong vibrations.
2. Description of the Related Art
Generally, a microwave oven carries out a cooking operation by receiving an alternating current (AC) voltage from a commercial AC power source, converting it into a high voltage, and driving a magnetron using the high voltage to generate microwaves to irradiate and cook foods.
Recently, a microwave oven has been developed to use a direct current (DC) power, such as a battery, as operating power, so as to install the microwave oven in mobile vehicles, such as cars or passenger ships.
The microwave oven using the DC power employs an inverter circuit to convert a DC voltage into an AC voltage required to drive a magnetron.
FIG. 1 shows a conventional microwave oven using DC power comprising a DC power source 1, such as a portable battery, a switching unit 2, an inverter unit 3, a high voltage transformer 4, a magnetron driving unit 5 and a magnetron filter box 6. The magnetron filter box 6 includes choke coils 8 and a feed-through condenser 9 installed therein, which constitute a low pass filter, so as to prevent fundamental waves of 2450 MHz, harmonic waves and noise generated by the driving of the magnetron 7, from radiating to the outside.
Ferrite cores (not shown) are inserted into the choke coils 8, and ends of the coils 8 wound around the ferrite cores are fixed through a welding process. Typically, a large inductance of the choke coils 8 favors reduction of noise, so the choke coils 8 are designed to be as large as possible.
However, vibration standards established by a standards organization, with respect to microwave ovens using DC power, are strict compared with those of a microwave oven using AC power for a home use. For example, a vibration standard of a microwave oven using DC power and installed in a car is limited to 3.3 to 4G. Accordingly, if a magnetron filter box used in the conventional microwave oven for a home use is applied to the microwave oven for a car, welding portions of choke coils may be easily damaged as the installation structure of the choke coils in the magnetron filter box is too weak to endure significant vibrations.
Therefore, there is a need for a microwave oven usable with DC power which satisfies the vibration standards as well as noise standards with respect to a magnetron filter box used in the microwave oven.
Accordingly, it is an object of the present invention to provide a microwave oven having choke coils which are installed inside and outside of a magnetron filter box so as to endure strong vibrations and eliminate noise to desired noise standards.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the above and other objects of the present invention, there is provided a microwave oven comprising a magnetron filter box having a magnetron, at least one first choke coil, and a feed-through condenser installed therein, and at least one second choke coil arranged outside the magnetron filter box and connected in series to the first choke coil, wherein the second choke coil, together with the feed-through condenser, constitutes a low pass filter.
According to an aspect of the present invention, the first choke coil is set to have an inductance smaller than that of the second choke coil.
According to another aspect the present invention, the first and second choke coils comprise corresponding first and second ferrite cores inserted therein, wherein weights of the first and second ferrite cores are proportional to the inductances of the first and second choke coils.
According to still another aspect of the present invention, the second choke coil is mounted on a printed circuit board connected to the magnetron filter box through a lead wire.